Test MethodEffects of ethanol content and temperature on the permeation of fuel through polyamide-12-based pipes

A new test method has been developed which enables the fuel permeation properties of polyamide-12 (PA-12) - based pipes to be investigated. Fuel lines were exposed to circulating fuel with equal volume contents of toluene, isooctane and 0, 25 or 85 vol.% ethanol for up to 6 months at 60-110 °C. The pipes were either of a single PA12-layer or a multi-layer type, the latter having a poly(vinylidene fluoride) barrier layer between two PA12 sections. With a Thwing-Albert cup attached to the fuel line, it was possible to expose a pipe-section to surrounding air running in a separate pipe loop at a controlled flow-rate. Gas/vapour samples were collected from this loop using a syringe and, subsequently, analysed with a flame ionization detector. It was observed in the case of multi-layer pipes that the presence of ethanol increased the permeability (average values) of the “total” fuel as well as of the individual hydrocarbons. In addition, the 60 °C fuel permeability (85 vol.% ethanol) increased after a high temperature (110 °C peak) cycle, whereas the ethanol-free fuel flux seemed to decrease.